Fixes/Features/Changes in 1.4.6:

* Universal binary for M1 (arm64) and Intel (x86) macs
* Minimum supported MacOS version set to 10.14
* Proper dark mode implementation adding MacOS vibrancy effects in background
* Supports saving two different pretty print themes (normal and dark mode)
* Remove double encoding of spaces in URL box (Issue #152)
* Adds environment variable substitution in headers, specified as ${VAR}
* Gatekeeper compatible signed release binary
* Minor UI arrangement tweaks
